Nd2Fe14B Phase Research Articles

Pengaruh waktu milling terhadap Sifat mikro struktur dan magnet dari NdFeB dengan proses Wet dan Dry milling

Making of magnets from NdFeB flakes by Wet and dry milling to determine the microstructure, physical and magnetic properties of the milling time variation is 16, 24, and 48 hours. The milling powder is then analysed to determine the particle size with PSA and XRD to determine the phase formed. Then the compacting process with isotropy printing for making pellet test samples with a pressure of 7 tons for 2 minutes. Then the pellet sample, given annealing temperature with a variation of 150 and 170 ̊C, then a measurement of magnetic properties with a Gauss Meter. The results obtained by the smallest optimum particle size with 48 hours of milling time at a diameter of 90% 4.7 μm, while the results of dry milling at a diameter of 90% amounted to 60.85 μm. The best method to get the smallest particle size is the Wet milling method. XRD results with Wet and Dry milling phases that appear only Nd2Fe14B phase. As milling time increases, the resulting density increases. The largest magnetic flux testing with dry milling method with 48 hours of milling time for temperatures 170 ̊C temperature obtained 468.5 Gauss and the addition of annealing temperature the magnetic properties of the material is getting better.

The reaction mechanism in the hydrothermal synthesis of Nd2Fe14B magnetic particles

Nd2Fe14B-based magnetic powders are essential in many applications. In this work, Nd2Fe14B hard magnetic particles were synthesised via hydrothermal techniques following a reduction–diffusion annealing process. The mechanism of Nd2Fe14B-particles formation was investigated via differential-scanning calorimetry and X-ray-diffraction; the results showed that Nd–Fe–B precursors of well-dispersed nanometre size were successfully synthesised via a hydrothermal reaction. The Nd–Fe–B oxides were composed of Fe2O3, NdFeO3 and NdBO3 (annealing at 900 ​°C) or amorphous BmOn (annealing at 700 and 800 ​°C). Reduction–diffusion (R–D) was a four-step process: first, the reduction of Fe2O3 to Fe occurred at 328 ​°C; second, NdBO3 was reduced to B and NdH2 at 341 ​°C; third, NdH2 and Fe were formed from NdFeO3 at 635 ​°C; and finally, the Nd2Fe14B phase was formed from NdH2, Fe and B at 659 ​°C. After removing the main by-product CaO, the coercivity of the as-synthesised Nd2Fe14B-based powder was 2.0 ​kOe. Analysis of the temperature-dependent magnetic properties revealed that coercivity was controlled by nucleation of the reversed magnetic domains.

Influence of a Reduction Process on the Phase Component and Magnetic Properties of NdFeB Magnetic Nanoparticles.

NdFeB magnetic nanoparticles with a main phase of Nd₂Fe14B have successfully been synthesized. The preparation includes the following processes. First, the NdFeB intermediate was synthesized by a wet-chemical method. The NdFeB intermediate was annealed at 800 °C, which resulted in the formation of an NdFeB oxide. Then, the NdFeB oxide was reduced into NdFeB nanoparticles by a second-step reduction annealing with a CaH₂ reductant. The second-step reduction annealing temperature was a key factor in preparing the NdFeB nanoparticles. A lower reduction temperature of 900 °C could not completely reduce the NdFeB oxide into Nd₂Fe14B. There were some residual unreduced nonmagnetic phases in the prepared materials, which resulted in obvious decreases of coercivity. A sufficiently high second-stage reduction temperature resulted in an increased reduction, and more of the Nd₂Fe14B phase could be obtained. In this work, nanoparticles with a uniform morphology and an increased Nd₂Fe14B phase could be obtained at an optimum reduction temperature of 940 °C, achieving a high coercivity of 5.4 kOe.

Effect of severe deformation on the microstructure and properties of Nd-Fe-B powders caused by hydrostatic extrusion

The commercial Nd-Fe-B (Magnequentch MQU-F42) powder was consolidated by hydrostatic extrusion at room temperature in three stages. The values of thru strain obtained after the stages, were 1.38, 2.27, 3.12. A high degree of deformation leads to local changes occurring in the microstructure of the material that negatively affects its magnetic properties. Mossbauer spectroscopy has shown that a new phase appears in the deformed material, most probably as a result of strong local defecting (amorphization) of the Nd2Fe14B phase. Rietveld analysis of the diffraction phase investigation results indicates that deformation leads to a clear fragmentation of the material grain and to the deformation (change of parameters) of the crystal lattice. The heating of deformed materials leads to a series of irreversible transformations that start at a temperature of about 200 °C. As a result, α-Fe is produced from the defected phase in the form of 3 nm crystallites. The release of free Fe changes the chemical composition of the 'defected phase', making it impossible for it to revert to the structure prior to deformation. It can be concluded that the structural changes occurring in Nd-Fe-B powders during severe deformation are irreversible and involve a permanent reduction in the magnetic properties of the material.

Micromagnetic simulation for optimizing nanocomposite Nd2Fe14B/[formula omitted]-Fe permanent magnets by changing grain size and volume fraction

Nanocomposite permanent magnets can achieve excellent magnetic properties due to the hardening of a soft phase by hard phase within the length of exchange coupling. The performance of exchange coupling nanocomposite magnets can be optimized through the design of appropriate microstructure by micromagnetic modeling. In this study, we performed a micromagnetic simulation for isotropic exchange coupling nanocomposite Nd2Fe14B/α-Fe permanent magnet in which grain sizes and volume fractions of magnetically hard Nd2Fe14B phase and soft α-Fe phase vary independently, ranging in grain size from 5 nm to 40 nm and in the volume fraction of α-Fe from 10% to 60%. When the grain size of the hard phase is 5 nm, and that of the soft phase is 10 nm, respectively, with the volume fraction of the soft phase of 30%, the highest (BH)max of 197 kJ/m3 can be reached. Furthermore, considering the effects of the grain sizes of the hard and soft phases, we suggest that the grain size of the hard phase plays a more critical role in enhancing maximum energy product (BH)max. The micromagnetic modeling with the variation of grain size and volume faction has been performed with a grain boundary (GB) phase. It was found that when the thickness of the GB phase is very small (~1nm), there is little difference between the simulated results with the GB phase and without GB phase. On the other hand, the coercivities and (BH)max decrease significantly due to the increase of soft phase when the thickness of GB phase is 5 nm.

Magnetic Structure and Nanomechanical Properties of Sintered Permanent Magnets Nd–Dy–Fe–B USC-20L

Using scanning electron microscopy (EDS analysis), magnetic force microscopy, and nanoindentation, a metallographic study of the magnetic structure and nanomechanical properties of sintered rare-earth magnets Nd–Dy–Fe–B of the USC-20L brand has been carried out (Ural Strip Casting Technology). The microstructure of the sintered Nd–Dy–Fe–B magnet of the USC-20L grade includes the following components: grains of the Nd2Fe14B phase are separated by lamellas of the phases enriched in neodymium. Inclusions Nd–29.1% Fe–6.2% C–2.2% O–1.4% Dy are located at the triple junctions of Nd2Fe14B grains. Inclusions Nd–4.5% Fe–9.1% O–6.7% C–4.5% Fe–2% Dy are along grain boundaries containing Nd and Dy oxides. The chemical composition of grains is Fe–25% Nd–6.9% C–1.6% Dy–1.4% B. It is found that, due to irregular grain growth, the interlayers of the enriched Nd phase are connected to each other in the region of grain junctions, causing a concentration of internal stresses and the appearance of a crack. The crack propagates along the grain boundary from one wetted joint of the grains to another, due to mechanical stresses. The phenomenon of intergranular wetting by a phase of Nd-enriched Nd2Fe14B/Nd2Fe14B grain boundaries is observed. It has been established that phases enriched with Nd can pseudo-incompletely (or pseudo-partially) wet such grain boundaries, i.e., form a nonzero contact angle along the grain boundaries and in triple joints. Based on the results of Magnetic Force Microscopy (MFM), a conclusion is made about the presence of a one-dimensional domain structure; domains cross grain boundaries. The presence of pores and inclusions of Nd and Dy oxides localized along grain boundaries is noteworthy. The average transverse domain size of the banded structure is ~1 μm, the energy of the domain wall γ ~ 14 kJ/m2, and the width of the domain wall δ ~ 0.6 × 10–9 m. The nanoindentation method is used to measure the values of nanohardness (H, GPa), elastic modulus (E, GPa), contact stiffness (S, N/m), elastic work (We, nJ) and plastic strain (Wp, nJ) in submicrovolumes of Nd2Fe14B grains. According to the measurement results, the minimum value of Nd2Fe14B grain adhesion Kint = 0.539 MPa m0.5 is estimated.

Microwave-Assisted Carbothermic Reduction of Discarded Rare Earth Magnets for Recovery of Neodymium and Iron Values

Neodymium-iron-boron (NdFeB) waste magnets consist of approximately 28% rare earth values in the form of the Nd2Fe14B phase. According to the results, carbothermic reduction through microwave irradiation of crushed magnets was observed to be promising for the separation of metallic iron and rare earth values. The effect of microwave exposure time and charcoal addition on the formation of different phases was evaluated. Carbothermic reduction (10% C) for 1.2 min raised the temperature of the sample to 990°C and resulted in the formation of iron balls with more than 85% purity. Higher exposure time favors the formation of the NdFeO3 phase, thereby encapsulating the rare earths, resulting in limited dissociation. Rare earth oxides with purity of more than 98% were recovered via a leaching and precipitation route. The microwave route was found to be superior to the conventional muffle furnace heating route with low energy consumption and metallic iron formation.

The improvement of magnetic property by grain refinement using magnetic field annealing crystalline (Nd0.8Pr0.2)2.2Fe12Co2B ribbons

The (Nd0.8Pr0.2)2.2Fe12Co2B ribbons were prepared by melt-spinning at a wheel speed of 15 m/s. The effect of magnetic field annealing treatment with 1 T in the temperature range of 573–723 K for 15 min on the magnetic properties including parameters of the coercivity, the remanence, and the maximum energy product ((BH)max) of (Nd0.8Pr0.2)2.2Fe12Co2B ribbons was investigated. The largest value of (BH)max among sample studied is obtained at 673 K for 15 min with 1 T. XRD result shows that samples are crystalline state and single Nd2Fe14B (2:14:1) phase is observed in both melt-spun ribbon and magnetic annealing sample at 673 K. The refined microstructure with an average grain size of 25 ± 3 nm is obtained in crystalline (Nd0.8Pr0.2)2.2Fe12Co2B melt-spun ribbons. The magnetic field annealing treatment with 1 T can further reduce the average grain size to 20 ± 1 nm. The mechanism of grain refinement is discussed from two aspects including the length-to-width ratio of a grain and the stress. The interaction domain structure is observed in both melt-spun ribbon and the sample annealed at 673 K with 1 T by Lorentz magnetic microscopy suggesting the presence of the exchange coupling between 2:14:1 grains. The grain-refined microstructure of magnetic annealing sample at 673 K strengthens the exchange coupling interaction leading to an enhancement of the remanence and the (BH)max, with a rise of 4% and 6%, respectively. The values of (BH)max of melt-spun (Nd0.8Pr0.2)2.2Fe12Co2B ribbon (141 kJ/m3) and annealed ribbon with 1 T magnetic field (150 kJ/m3) are both larger than that of some Dy-containing Nd-Fe-B permanent alloys with an improving range of 7%-74%.

Investigation of the magnetic properties and fracture behavior of Nd–Fe–B alloy powders during high-energy ball milling

In this work, Nd–Fe–B alloy powders are fabricated via high energy ball milling and their fracture behavior and magnetic properties are investigated at different milling times. The powder characteristics (particle shape, size, size distribution, and microstructure) and magnetic properties of the Nd–Fe–B alloys are systematically analyzed. The initial spherical Nd–Fe–B powder is cracked/crushed even after a short period of milling (30 s) due to the high impact energy generated during high energy ball milling. These randomly cracked polygonal-shaped powders are fragmented after 5 min of milling and converted to fine powders. Interestingly, the fine particles after milling for 5 min are conducive to agglomeration at longer milling times (20–60 min) and formed spherically-shaped agglomerated powder. Additionally, the sphericity of the powder increased to 92% by re-pulverization and agglomeration at 60 min. The milled powder shows the Nd2Fe14B phase, and the x-ray diffraction patterns exhibit peak broadening with increasing milling time, clearly confirming the powder refinement behavior by high energy ball milling. The magnetic properties of the milled powders are systematically investigated and their behavior is elucidated as a function of the milling time.

Electrochemical synthesis and magnetic properties of Nd-Fe-B-Tb nanowires

Nd-Fe-B-Tb nanowires were synthesized in AAO templates by electrodepositon through doping Tb3+ into Nd-Fe-B solution. The as-deposited nanowires are composed of Fe and amorphous phases, showing soft magnetic properties. Annealing makes Nd-Fe-B nanowires consist of Nd2Fe14B, Fe3B and NdB4 phases and exhibits hard magnetic characteristic due to the formation of hard Nd2Fe14B, Fe3B phases. After adding Tb3+, some new (Nd,Tb)2Fe14B, Tb2Fe14B, Fe3Tb and TbB50 phases, form in annealed nanowires. The existence of (Nd,Tb)2Fe14B and Tb2Fe14B phases with high anisotropy fields, the interface elastic coupling effect between different phases and the coherent phase interface increases the coercivity and remanence. Nd-Fe-B-Tb nanowires exhibit the optimal comprehensive magnetic properties at 0.05 mol/L Tb3+ concentration due to the highest content of Tb2Fe14B phase.

Studying the Effect of Praseodymium Pr Substituted Nd<sub>2</sub>Fe<sub>14</sub>B Alloys on its Magnetic Anisotropic Properties Prepared by Arc Melting

Nd2Fe14B permanent magnet manufacturing technology in some developing countries is still relatively difficult because it is constrained by limited equipment facilities and dependence on imports of raw materials. In the context of efforts to build national independence, the concrete step is to try to study the process of making permanent Nd2Fe14B magnets with conventional facilities and technology. In this research an attempt was made to make and characterize Nd2Fe14B permanent magnets substituted with praseodymium Pr metal using conventional technology through the arc melting method. The success parameter of the results of this sample making is the formation of the Nd2Fe14B phase in the sample. The formation of this phase can be fundamentally studied the number of mass fractions of formed phases and structure crystallography using X-ray diffraction facilities and is supported by spectroscopy facilities and their magnetic properties. So the purpose of this research in general is to study the manufacturing process and the fundamental formation of the phases of the NdPrFe14B sample making through the arc melting method, while specifically wanting to know the relationship between phase analysis and the magnetic anisotropic properties of NdPrFe14B. The coercivity field appears to increase significantly after the sample is substituted with Pr and has a fairly small crystallite size distribution. So it was concluded that the presence of Pr was able to withstand the growth of grain, causing the anisotropic magnetocrystalline field to increase.

The effects of AB2 (A = Zr,Hf,Ti) additions on the free-iron content in ingots with the initial composition of Nd2.2Fe14B1.1

Additions of zirconium diboride (ZrB2), to small scale (~1 g) arc-melted (AM) and larger scale (5 kg) book mould (BM) cast alloy with the composition Nd2.2Fe14B1.1 (near to stoichiometric Nd2Fe14B) have been shown to be a very effective means of eliminating the free-iron content, which is present as a result of the peritectic nature of the Nd2Fe14B phase. The effect of zirconium diboride in reducing free-iron content has been determined (1) magnetically by means of the Honda-Owen plots on the BM alloys and (2) by image analysis using scanning electron microscopy for both AM and BM alloys. Generally, for the BM alloys, both sets of measurements exhibited good agreement with a progressive reduction in the free-iron content with increasing additions of ZrB2. Without any subsequent homogenisation treatment, zero free-iron was achieved in the AM and BM cast condition, after an addition of just 1 mol% of ZrB2. Closely similar behaviour was observed with up to 1 mol% additions of the other Group 4 diborides, TiB2 and HfB2. High resolution scanning electron microscopy indicated that the diborides were embedded largely within the areas of Nd-rich material.

Phase Structure, Microstructure, and Magnetic Properties of (Nd-Ce)13.4Fe79.9B6.7 Alloys

Phase structure and microstructure of (Nd1-xCex)13.4Fe79.9B6.7 (x = 0.0–1.0) alloys that were prepared via the arc-melting method were studied experimentally in this work. The results reveal that (Nd1-xCex)13.4Fe79.9B6.7 alloys annealed at 1173 K for 360 h are a single (NdCe)2Fe14B phase with the tetragonal Nd2Fe14B-typed structure (space group P42/mnm). The formation of continuous (NdCe)2Fe14B solid solution phase in annealed (Nd1-xCex)13.4Fe79.9B6.7 alloys was confirmed. On the other hand, magnetic measurements exhibit that the coercivity, remanence, maximum magnetic energy product, and Curie temperature of (Nd1-xCex)13.4Fe79.9B6.7 ribbons that were fabricated by melt spinning technology decrease gradually with increasing Ce content, which results from the substitution of Nd by Ce in Nd2Fe14B phase due to inferior intrinsic magnetic properties of Ce2Fe14B phase.

Fabrication and growth of c-axis textured Nd2Fe14B thin films by high-rate sputtering

To apply Nd–Fe–B thin films for mass-produced heat-assisted magnetic recording media, we investigated the high-rate sputtering conditions required to obtain c-axis textured Nd2Fe14B thin films and analyzed the growth mechanism. Magnetization curves indicated that higher substrate temperatures and sputtering rates resulted in a higher degree of perpendicular magnetic anisotropy; a Nd–Fe–B layer deposited at a substrate temperature (Tsub_0) of 600 °C and a sputtering rate (Rsp) of 2.6 nm/s had the easy axis perpendicular to the film plane. The dependence of the magnetic properties on the sputtering rate was due to a decrease in the substrate temperature during sputtering; there was a threshold for obtaining a high squareness ratio. X-ray diffraction analysis and transmission electron microscopy (TEM) images showed that the c-axis textured Nd2Fe14B crystal phase was formed in the Nd–Fe–B layer deposited at Tsub_0 = 600 °C and Rsp = 2.6 nm/s, which resulted in the highly perpendicular magnetic anisotropy. In addition, the TEM images showed a layer of Nd2Fe14B with no obvious lattice fringes near the interface between the Nd–Fe–B layer and Mo underlayer, while the lattice fringes of the Nd2Fe14B phase were not parallel to this interface but gently curved along the Mo cap layer. We propose that the c-axis orientation was achieved by the rotation of the c plane, which has the lowest surface energy in the Nd2Fe14B phase, toward the vacuum-side surface during sputtering.

Fabrication and characterization of 1-dimensional neodymium-iron-boron fibers using new reduction-diffusion process

A novel method for the synthesis of neodymium-iron-boron (Nd-Fe-B) fibers is demonstrated in this study by adopting three continuous processes: electrospinning, step heat treatment, and a new process comprising facile reduction-diffusion. The structural and crystalline studies revealed that as-spun precursor fibers were transformed into FeNdO3, Fe2O3, and NdBO3 phases by non-isothermal heat treatment; further, the oxide mixture fibers were reduced to a single Nd2Fe14B phase by the facile reduction-diffusion process. A facile reduction-diffusion process in this paper can obtain Nd2Fe14B fibers without brokenness; this is because it leads to the formation of a thin salt layer on Nd2Fe14B fiber surface when reacting to by-product CaO granules. The BHmax of Nd2Fe14B fibers was exhibited by 3.34 MGOe. To our knowledge, this is the first attempt to fabricate 1-D Nd2Fe14B fibers successfully using a new reduction-diffusion process. This work provides a simple way to prepare 1-D hard magnetic Nd-Fe-B fibers with excellent shape anisotropy attributed to a high aspect ratio.

The influences of annealing on surface morphology and microstructure of NdFeB thin film

NdFeB thin films are produced by DC magnetron sputtering. The influences of annealing on surface morphology and microstructure of NdFeB thin films are studied in this paper. The result shows that the formation of Nd2Fe14B is prevented by depositing film directly on the substrates. Nd2Fe14B phase exists in crystalline films with Mo as a buffer layer and protective layer. Mo is a good material for being a buffer layer and protective layer. The (110) oriented texture of Mo is formed on (100) mirror polished Si after annealing. The deposited films are amorphous. SEM results show that the grain size is fine and uniform after annealing. Atomic Force Microscope investigation reveals that the film is smoother and denser after annealing. It is found that the films are still amorphous with annealing temperature below 400 °C, and the films begin to crystallize after annealing at 500 °C; the films annealed at 600 °C are fully crystallized.

Additive manufacturing of heavy rare earth free high-coercivity permanent magnets

Laser based powder bed fusion is a promising manufacturing method that can be used for the fabrication of hard magnets such as NdFeB with nearly any given geometrical shape. However, the weak performance, e.g., low coercivity, of the 3D-printed magnets currently hinder their application. In this work, we demonstrated a proof-of-concept of powder bed additive manufacturing of heavy rare earth free NdFeB magnets with technologically attractive coercivity values. The 3D-printed NdFeB magnets exhibit the highest (up-to-date for the additively manufactured magnets without heavy rare earth metals) coercivity values reaching μ0Hc = 1.6 T. The magnets were synthesized using a mixture of the NdFeB-based and the low-melting eutectic alloy powders. The essential function of the eutectic alloy, along with binding of the NdFeB-based magnetic particles, is the significant improvement of their coercivity by the in-situ grain boundary (GB) infiltration. The fundamental understanding of the magnetization reversal processes in these 3D-printed magnets leads to the conclusion that the excellent performance of the additively manufactured hard magnets can be achieved through the delicate control of the intergrain exchange interaction between the grains of the Nd2Fe14B phase.

Magnetic properties enhancement of hot-deformed NdFeB magnets by two different methods of CeNdCu diffusion

Two different ways were used to control the distribution of cerium for the enhancement of coercivity. One was by coating CeNdCu in the prepared magnet and annealing to make CeNdCu diffuse into the grain boundary to increase the coercivity, the other was by mixing CeNdCu with initial magnetic powders and then preparing the hot-deformed magnet. The SEM-EDS result indicates that cerium diffuses more easily into the main phase by the mixing way, while cerium is mainly distributed in the grain boundary via the coating way. The heat-treatment process may be one of the dominant influencing factors for the distribution of Ce. Multi-steps heat treatment in the mixing way, consisting of hot-pressing, hot-deforming and post heat process, easily introduces Ce into the main phase Nd2Fe14B, which forms the Ce2Fe14B shell resulting in the decrease of HA. But the coating way can ensure uniform dispersion of Ce in the grain boundary, which leads to the high coercivity.

The Influence of Heat Treatment on the Phase Structure of the Nanocrystalline (Nd10Fe67B23)95Nb5 Alloy Ribbons

The main goal of present paper was to study of phase composition of nanocrystalline (Nd10Fe67B23)95Nb5 ribbons prepared by melt-spinning technique with different velocity of the copper wheel. Samples in the as-cast state obtained using speed 5 and 10 m/s had nanocrystalline structure. In case of samples prepared by with speed of copper Wheel 15 and 35 m/s were fully amorphous. In the DSC curve, the two minima corresponding to crystallization of the Nd2Fe23B3 and Nd2Fe14B phases were detected. The coexistence of three phases: Nd2Fe14B, Nd2Fe23B3 and Nd1+εFe4B4 were detected. Higher temperatures of annealing caused crystallization of α-Fe phase. The XRD results were confirmed by the Mössbauer studies. Keywords: hard magnetic materials, phase structure, Mössabuer spectroscopy

Effect of Al/Cu on the magnetic properties and microstructure of Nd-Fe-B sintered magnet by diffusing Pr-Tb-(Cu, Al) alloys

Grain boundary diffusion process (GBDP) using Pr60Tb10Cu30−xAlx (x = 0, 5, 15, 25, 30, atomic fraction) alloy ribbons, named as A0–A30 alloys, was applied to high maximum energy product (BH)max Nd-Fe-B sintered magnet. After diffusion, coercivity (Hci) of A0 magnet is significantly enhanced from the original 11.4 kOe to 19.5 kOe with remanence (Br) decreasing from 14.65 kGs to14.32 kGs, which is mainly attributed to magnetic hardening effect by Tb-rich shells. With substituting 5 at% Al for Cu, the Hci and Br of A5 magnet are simultaneously enhanced by the homogenized distribution of Tb-rich shells and the reduced interface energy of Nd-rich phase and Nd2Fe14B phase. The highest coercivity of 22.4 kOe is obtained for A25 magnet by further strengthening magnetic isolation of Nd2Fe14B phase, however, which results in a drastic decrease in Br due to the increased fraction of Nd-rich phase and too much substitution of Al for Fe in Nd2Fe14B phase. Therefore, the Hci (kOe) + (BH)max (MGOe) reaches to the peak value for A5 magnet. Also, it is proven that Cu/Al co-addition can effectively improve Tb diffusion efficiency by modifying intergranular Nd-rich phase.